Pneumatic powder feeder



Filed Jan. 20, 1955 G. R. SPIES, JR, E'l'AL PNEUMATIC POWDER FEEDER 5 Sheets-Sheet 1 INVENTORS GEORGE R SPIES Jr.

. 'HARRY HOOPFR ATTORNEY Jan. 28, 1958 I y can. sPlEs, JR., ETAL 2,821,439

' PNEUMATIC POWDER FEEDER Filed Jan. 20, 1955 v 5 Sheets-Sheet 2 INVENTORS GEORGE R SPIES Jr.

HARRY HOOPER ATTORNEY "FIG, 6

Jan. 28, I958 Filed Jan. 20, 1955 PRESatiURE FOR VARIOUS THROTTLE SETTINGS G. R. SPIES, JR, ETAL PNEUMATIC POWDER FEEDER HBCIMOd 5 Sheets-Sheet 3 "an/s81 3131a 0335 aaumod GEORGE R SPIES Jr. HARRY HOOPER ATTORNEY 2 1958' e. R. SPIES, JR., ETAL 2,821,439

PNEUMATIC POWDER FEEDER Filed Jan. 20, 1955 5 Sheets- Sheet 4 III v vmvsu'rons' GEORGE R SPIES Jr. HARRY HOQPER BY MM ATTORNEY Jan. 28, 1958 a. R. SPIES, JR., ETAL 2,821,439

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H39 Ind-u HIV INVENTORS- 1 GEORGE- R SPIES Jr- BY HARRY HOOPER ATTORNEY United States Patent PNEUMATIC POWDER FEEDER George R. Spies, Jr., Murray Hill, and Harry Hooper, Westfield, N. J., assignors to Air Reduction Company, Incorporated, New York, N. Y., a corporation of New York Application January 20, 1955, Serial No. 482,984

8 Claims. (Cl. 302-53) This invention relates to a method of and apparatus for dispensing finely-divided materials, and more particularly to an improved powder dispenser and its method of operation wherein a powdered material is entrained in a gas stream and moved to a point of use.

In certain thermochemical operations on iron and steel, it is desirable to introduce quantities of finely-divided material, such as iron powder or iron-aluminum powder, into the reaction zone of the preheat and cutting oxygen streams and to have a portable powder dispensing or feeding apparatus which is capable of moving either a single stream of powder gas or to move several independent streams simultaneously into the aforementioned reaction zone.

It is also desirable to have independent control means for each stream and to have a powder dispensing apparatus which is of relatively simple construction but adapted to feed several difierent types of finely-divided material such as iron powder, sodium bicarbonate, or aluminumiron mixtures.

There is also a need for an improved inexpensive pneumatic powder feeder which is capable of moving varying quantities of calcium carbide and similar treating agents or mixtures thereof from a container through a conveying line and injection tube to beneath the surface of molten metal, such as cast iron.

It is therefore an object of this invention to provide an improved powder dispenser and a method of operation wherein a powdered material is entrained in one or more separately controlled flowing gas streams and conducted at a predetermined fixed rate to one or more points of use.

Another object of this invention is to provide a powder dispenser wherein the gas pressure maintained within the hopper is greater than the pressure supplied to the powder inductor assembly.

A further object of this invention is to provide a meth 0d of and apparatus for dispensing powdered material such as iron powder at a feed rate from about between four and ninety pounds per hour.

Another object of the instant invention is .to provide an improved inexpensive pneumatic powder feeder for injecting the calcium carbide type of treating agents, at varying rates up to about fifty pounds a minute, beneath the surface of molten metal.

A still further object of this invention is to provide a novel powder feeder which incorporates into a single unit a plurality of individual valve controlled powder inducting means and powder outlet conduits wherein a decrease of gas flow through the outlet conduits via the valve control means effects an increase in the powder feed rate.

Other objects of this invention are to provide a powder dispenser with an improved powder inductor assembly which is readily removable, to provide an inductor assembly which maintains a supply of powder of substantially uniform weight above the entrance orifices of the outlet conduits regardless of the quantity of powder withice in the dispenser or the rate at which the powder is being discharged, and to provide an assembly in which the entrance orifices of the outlet conduits are below the powder inlet ports of the inductor assembly.

The accomplishment of these and other objects and advantages of the invention will be pointed out or will become apparent from the following description and the accompanying drawings.

Fig. 1 is a side elevational view, partly broken away and in section, showing a preferred embodiment of the invention arranged schematically for cutting a metal body.

Fig. 2 is a front elevational View of the gas supply and control assembly shown at the left in Fig. 1.

Fig. 3 is a top view of the powder dispenser shown in Fig. 1.

Fig. 4 is an enlarged partially-sectional and side elevational view, showing the powder inductor assembly of Fig. 1 device.

Fig. 5 is a partially cross-sectioned top view of the powder inductor assembly shown in Fig. 4 and taken along line B-B which corresponds to line A-A in Fig. 1.

Fig. 6 is a graphical representation of the relation between the iron powder feed rate and the regulator pressure for various throttle settings of the instant invention when feeding through a single outlet.

Fig. 7 is a graphical representation of the relation between the iron powder feed rate per outlet and the regulator PICSSUIB for various throttle settings when the instant invention was feeding through two outlets.

Fig. 8 is a partially cross-sectioned side view of another preferred inductor assembly and adjacent parts and schematically shows the invention arranged to feed a treating agent into molten metal.

Fig. 9 is a graphical representation of various relations existing when a feeder using the Fig. 8 inductor was used to feed calcium carbide.

Fig. 10 is a graphical representation of various rel tions obtained when the Fig. 8 feeder was used for feeding calcium carbide through a smaller conduit than was used in establishing the Fig. 9 relations.

Referring to Fig. 1, the powder dispensing unit shown therein comprises three main sub-assemblies, a closed vertical cylindrical hopper H, a readily removable and replaceable powder inductor assembly P, and a gas supply and control assembly S.

As shown in Fig. 1 and Fig. 3, the vertical cylindrical hopper assembly H, is provided with a pair of outwardly extending handles 1 oppositely secured to the cylindrical hopper wall 2 intermediate its ends, and is supported in any suitable manner as for example by legs 3.

The hopper assembly H also has two large bolts 4 and 4 externally and oppositely secured to wall 2 in such a manner that the threaded end portions of these bolts extend above the rim 5 of the hopper wall. Large sized wing nuts 6 engage the threaded end portion of these bolts and thereby furnish clamping means for the hopper cover 7. When the hopper cover is clamped in place, a sealing gasket 8 cemented to the under surface thereof rests upon the edge of the hopper rim 5 and assures a gas tight seal. The hopper cover while being essentially circular in shape as shown in Fig. 3 is provided with a pair of slotted projections 9 and 10 which extend toutwardly from opposite sides of the hopper cover. These projections straddle the threaded end portions of the bolts 4 and 4 and furnish bearing surfaces 11 upon which the wing nuts 6 are seated. Removal of the cover may be easily and quickly accomplished by merely pivoting it about the bolt 4 so that the slotted clear of the bolt 4'.

A removable brass screen 13 is supported in the upper portion of the :hopper by means of a flange 14 secured projection 9 swings 3 to the inside of the hopper wall 2. This screen serves the dual purpose of screening any large foreign substances and agglomerated powder from the charge and subsequently acts as a retainer for a supply of conventional desiccant material which maintains a thoroughly dry atmosphere within the hopper.

An internally threaded gas inlet sleeve 16 is mounted in the hopper wall 2 below the screen 13 for external connection with the gas supply and control assembly S, to be later described, and for internal connection with the pressure inlet tube assembly 17. The pressure inlet tube assembly 17 comprises a half union coupling 18, a sleeve for threaded engagement therewith, and a flare nut 20 for fastening the pressure inlet tube 21 to the sleeve. The pressure inlet tube 21 is bent in such a manner as to terminate in a depending leg 22. This arrangement precludes the possibility of the pressure inlet tube becoming clogged at the time when the hopper is being charged with powder 24.

The gas supply and control assembly S is connected by means of a flexible hose 25 to a high pressure gas supply line 26 having a shut off valve 27 through a gas pressure regulator 28 with the usual pressure indicating gauge 29 and a flow meter 30. The gas supply and control assembly S includes a cock valve 31 having threaded connection with the horizontal outwardly extending nipple 32 of the cross-joint 33. To the upwardly extending nipple 34 of the cross-joint 33 there is attached a relief valve 35 which is provided for protection against the development of dangerous pressures within the hopper H. The inwardly extending nipple 36 positioned opposite the gas inlet cock valve 31 makes threaded connection with the gas inlet sleeve 16 and so provides the hopper H with gas. As shown in Fig. 2, the depending nipple 37 of the cross-joint 33 has secured thereto a connecting T 38, the horizontal branch of which leads to a drain cock 39. The other branch of connection T 38 is secured to a conducting tube 40 which in turn terminates in a second connection T 41. From the connecting T 41, branch conduits 42 and 43 establish separate carrier gas lines. Each line is equipped with a throttle valve 44 and a connecting conduit 45 which leads to the powder inductor assembly P, centrally located at the hopper base 46.

Referring now to Fig. 4 and Fig. 5, it can be seen that a pair of unrestricted powder inducting conduits 47 are transversely secured across the hollow main body portion 48 of the assembly P and make connection through passageways with the aforementioned conduits 45. The inducting conduits 47 are provided with powder inlet orifices 49 centrally located in the bottom thereof and each orifice is surrounded with a depending tubular shield 52 fixedly secured to the respective conduit. Shield 52 depends 0.250 of an inch from the bottom of pipe 47 and has an internal diameter of about 0.180 of an inch. Shield 52 and conduits 47 are made from stainless steel.

As shown in Fig. 5, the inducting conduits 47 terminate in a block 53 which is equipped with oppositely extending hose couplings 54. Passageways 55 provide gas connection between conduits 47 and their respective hose couplings. Again referring to Fig. 4, it can be seen that the broken-away hollow main body portion 48 of the inductor assembly P is capped at the bottom with a conventional pipe cap 56. This cap is easily removed to permit inspection of the inducting mechanism and extraction of any foreign material or other agglomerate particles without requiring the removal of the inductor assembly from the hopper. However, the hollow main body portion 48 of the inductor assembly P has an externally threaded neck 57 which engages an internally threaded flange 58 centrally depending from the hopper bottom 46 (seeFig. 1). This construction permits the ready removal of the entire inductor assembly from the hopper, when and if such removal is desired. There is also incorporated in the inductor assembly P a hollow anti-bridging dome 59 which effectively penetrates the powder 24 in the hopper H and prevents the powder from bridging. The upper portion of the hollow anti-bridging dome, as shown in Fig. 4, has a pointed surface 62 about which the powder may gravitate. The lower wall portion 63 of the hollow anti-bridging dome is provided with powder inlet ports 64 which are positioned slightly above the level of the hopper bottom 46 as shown in Fig. 1. There is a shallow annular recess around the dome 59 below the level of the hopper bottom. This recess is formed by flange 58, wall 63 of the dome and plate 65 which is attached to the top of member 48. The inlet ports 64 allow the powder to enter the hollow dome and drop into the main body portion 48 of the inductor assembly P above the inducting conduits 47. Regard less of the quantity of powder within the hopper or the feed rate at which the powder is being discharged, the weight of powder above the shield and entrance orifices of the powder inducting conduits remains substantially constant throughout the operation. It is to be noted that this quantity of powder is relatively quite small. The main body portion 48 is a brass nipple about 5 inches in length and having an internal diameter of about 1.35 inches. The orifices 49 have a diameter of 0.0935 of an inch. The internal diameter of conduits 47 is about 0.180 of an inch.

A flange or plate 65 is fixedly secured to the outside of wall 63 of the anti-bridging dome 59 below the powder inlet ports 64 and is further secured, as by press fit, within the neck 57 of the hollow main body portion of the inductor assembly P.

As shown in Fig. 1, the present invention can be used to convey iron powder and other suitable materials to a thermochemical operation being performed on a workpiece W, such as a steel plate. The torch T schematically represents conventional cutting or scarfing torches which are constructed to feed iron powder such as shown in U. S. Patent #2,627,826 (issued to Meincke on February 10, 1953). A long flexible torch hose 66, usually less than twenty-five feet in length, is connected to the pneumatic powder feeder by means of hose coupling 54. A schematic control valve 67 is shown as the means for controlling the flow of the gas-powder stream to the torch. Oxygen and acetylene control and supply means have been omitted in the interests of clarity.

In operation, the hopper cover is positioned to permit the charging of the hopper. The powder is poured through the screen 13 where large foreign and agglomerate particles are retained and subsequently removed. An envelope of desiccant material 15 is then placed in the screen and the cover is again secured in place. The unit is now ready for operation and the high pressure line valve 27 is opened and the desired hopper pressure set by regulator 28. Cock valve 31 is opened to admit the gas to the hopper H and to conduit 40. If the throttle valves 44 are fully opened at this time the pressure within the hopper H and the pressure supplied to the inductor assembly P are not at equilibrium since the valves 44 provide some restriction or throttling. Thus, a zero setting provides a slight pressure differential and a minimum feed rate from about between 2 to 8 pounds of iron powder per hour per torch, depending on the setting of regulator 28. If desired, valves could be used which did not throttle when fully open. As the throttle valve or valves 44 are closed, the pressure in the inductor assembly P is reduced and the hopper pressure is increased, thus affecting a greater pressure differential between the hopper H and the powder inductor assembly P. Each succeeding throttle closure correspondingly increases the pressure differential.

In using the Fig. 1 device for iron powder feeding, dry air or nitrogen at less than 25 p. s. i. g. is introduced into the feeder inlet from the pressure regulator. A portion of this gas is directed into the hopper, but the majority of flow follows the path through the concentrating valve 44 and inductor tube 47. Although a very small flow of gas probably does take place through the powder and eventually through the inductor port and outlet, it is believed that the gas over the top of the powder is mostly static and therefore at a pressure essentially the same as that where the incoming stream divides. The flow which passes through the concentrating valve 44 is appreciable and by imposing a throttle condition at this valve a pressure drop is developed. It is apparent that this pressure drop is ultimately reflected in a pressure difference between the inside and the outside of the inductor tube and specifically across the inductor port 49. This pressure difit'erence across the inductor port causes powder to flow up in shield 52 and through the port and the powder thus fed is picked up by the gas flowing through the inductor tube and conveyed to the cutting torch T. The amount of powder which will feed is dependent upon the amount of pressure drop across the inductor port and the size of the port, but since the latter is fixed, feed depends solely on the pressure drop. Hence, the feed rate is adjustable by means of the regulator pressure setting and the concentrating valve throttle. It should be noted that the powder under the shield 52 does not have even the weight of the powder in tube 48 bearing directly down upon it.

As shown by the graphical relation between the iron Powder feed rate and the regulator pressure illustrated in Figs. 6 and 7, each subsequent throttle closure is also accompanied by an increase in the powder feed rate, providing of course that the regulator pressure is maintained substantially constant. For example, in both Figs. 6 and 7, it can be noted from the curves pertaining to the no throttle or zero setting, /2, fie, and throttle setings, that there is a marked powder feed rate increase for any particular regulator pressure setting.

The powder cutting torch T used with the instant invention, as heretofore mentioned, may be of any standard design and may be used in the usual manner known to those skilled in the art. In most torches of this type the cutting oxygen and powder entrained gas streams have a sequential valve control mechanism. To commence cutting or scarfing, the operator merely lights his torch and retracts the torch trigger. This initiates the flow of cutting oxygen and the powder laden gas stream. When the powder (most of which is less than 100 mesh and all less than 20 mesh Tyler) within the hopper has been exhausted, the operator ceases the operation by releasing the torch trigger and extinguishing the flame. Cock valve 31 is then closed shutting otf all pressure to the hopper H and the gas supply and control assembly S. The drain cock 39 is then opened to reduce the pressure in the system to atmospheric pressure so that the hopper cover may be easily removed and the hopper recharged in the manner heretofore described. After the drain cock has been closed and the hopper recharged, the cock valve 31 may be reopened to readmit pressure to the system. The torch is once again ready for operation, and since the gas pressure to the hopper H and to gas supply and control assembly S has been shut off without changing either the inlet pressure or the throttle valve settings, the same feed rate may be readily reestablished. Equal or different feed rates through the two conveying lines can be accomplished. The preferred pressure differential for iron powder feeding is less than 20 p. s. i. g. Inlet gas pressure should exceed about 5 p. s. i. g. It is apparent that the throttle valve permits a range of feed rates at a given regulator setting.

Precise feed rates can be established for each external conveying system and torch or other apparatus used with the instant feeder by plotting the throttle settings and regulator pressures against feed rates as shown in Figs. 6 and 'I.

With reference to the Fig. 1 apparatus, it is to be noted that the anti-bridging construction minimizes the effect of the weight of the powder in the hopper on the feed rate.

.6 Whether the hopper is fuller almost empty, the feed rate remains practically constant. Further, the inlet shut-off valve permits the feeder to be shut off without changing established regulator pressure settings as when shutdowns for recharging occur. Feed rates per outlet of 4 to 90 pounds of iron powder an hour per out-let are easily established. The preferred rate is 10 to 60 pounds an hour at flow rates of 40 to 100 cubic feet of gas an hour. The maximum inlet pressure is less than about 25 p. s. i. g.

Referring now to Fig. 8, an alternate embodiment of the invention which is adapted to feed finely-divided calcium carbide through a conduit to an injection tube which injects the carbide beneath the surface of molten iron will be described. Fig. 8 is a schematic showing in so far as the gas supply and control arrangement and the injection set-up are concerned and includes a partially cross-sectioned and broken-away showing of the powder inductor assembly in relation to the schematic arrangement. The hopper and the connection thereto of the inductor have been omitted since they are the same in essence as the Fig. 1 showing. It is to be appreciated, however, that the Fig. 8 inductor is attached to a hopper essentially the same as shown in Fig. l and can have a similar anti-bridging device. The Fig. 8 gas supply system is connected to a gas supply which corresponds to the supply available in pipe 25 of Fig. 1.

The alternate Fig. 8 pneumatic powder feeder differs from that shown in Fig. l principally in that a gas bypass around the inductor is provided and in that the internal par-ts of the inductor are made from standard pipe fittings. Unlike the Fig. l apparatus, the gas-powder stream is discharged from its consuming device (a graphite injection tube immersed in molten iron) against a static pressure head, not against what is essentially atmospheric pressure. For this reason, the bypass connection is made so that the hydrostatic head of the metal can be overcome prior to beginning injection and entrance of metal into the tube prevented.

In the Fig. 8 embodiment a connecting T 70 is connected to a gas supply line 69 (like 25' of Fig. 1) so that a bypass line 71 may be connected upstream of valve 76. This shut-off valve 76 corresponds to cock valve 31 in Fig. 1 and controls the gas supply to both the hopper and the inductor assembly. By-pass line 71 is provided with a shut-off valve 72 and terminates in a three way valve 73 downstream of the inductor assembly 74. This arrangement establishes a passage through which a stream of gas may be supplied to the graphite injector tube 75 to prevent molten metal entering said tube when it is submerged beneath the surface of the metal before a gas-carbide stream is injected. The other branch of connecting T '70 leads to shut-off valve 76 and then to a second connecting T 77. A gas line 78 extending from the vertical branch of this T is equipped with a shut-off valve 79'and connects to the top of the hopper (not shown). A second gas supply line '80 which is equipped with a throttle valve 81 leads from the other branch of T 77 to the powder inductor assembly '74. Valve 81 corresponds to valves 44 in Fig. 2.

The powder inductor assembly shown in Fig. 8 includes a cylindrical inductor body 82 having a transverse gas inlet line mounted therein and a reducing T 83 secured to the terminal end thereof such that the T is centrally located within the cylindrical inductor body 82. A powder outlet conduit 87 of slightly greater cross-sectional area than the powder inlet line 80 is also transversely mounted in the cylindrical inductor body 82 and makes threaded connection with the slightly enlarged nipple 85 of the reducing T 83. Nipple 86 depends from the central portion of the reducing T 83 and retains threaded sleeve 88 which restricts the upward flow path. A reducing coupling 90 engages the sleeve 88 and a powder shield-or inlet conduit 92 is connected to the opposite end of coupling 90. A tubular body 93 depends from the cylindrical inductor body 82 and is capped at the bottom with a conventional pipe cap 94, thereby forming the bottom of a hollow chamber 95 from whence the powder may be inducted. Inductor body 82 was attached to the hopper by conventional means whereby subchamber 95 was completely formed. A long feed line such as a flexible hose 97 extends from valve 73 to injection tube 75.

When the alternately-designed Fig. 8 apparatus is used to handle calcium carbide and inject it beneath the surface of molten metal a slightly different method of operation is often required than in with iron powder feeding to a torch such as previously described. The gas inlet line 69 is connected to a source of metallurgically inert gas such as nitrogen, while the shut-off valves 76 and '72 are in the closed position. Gas is then admitted to the hopper through shut-off valves 76 and 79 and valve 72 is opened. The three way valve 73 has been adjusted to establish a flow passage between supply line 71 and injection tube 75 and not pipe 87. The gas in pipe 71 and hence tube 75 is such as to overcome the hydrostatic pressure of the molten metal in the injection tube and so prevents entrance of metal. Next the tube is inserted beneath the surface of the molten metal. Throttling valve 81 is then adjusted as desired and three way cock valve 73 is subsequently rotated to a position so that the flow of gas through the by-pass line is interrupted and the flow of powder to the injector tube 75 via the inductor assembly 74 and outlet line 87 is initiated. In order to cease operation, the operator merely returns the three way cock valve 73 to its original purge position and then withdraws the injector tube from the molten metal. The picking-up of the finely-divided calcium carbide by nitrogen in the inductor and moving thereof through a 20-25 flexible hose are identical with the functioning previously described. It is to be noted that nipple 92 and the restriction provided by sleeve 88 correspond to and function as the shield 52 and orifice 49 in Fig. 4. Further, the T 83 provides an essentially unrestricted passage like inductor tube 47.

Figs. 9 and 10 are charts of tests made with the Fig. 8 apparatus using carbide and air and show the relation be tween cubic feet of air per hour and the feed of carbide in pounds per minute at various settings of throttle valve 81. Zero throttle, of course, does not mean that no gas is flowing to the inductor but rather means a certain throttle setting, the valve itself when open provides some restriction to flow and pressure reduction. The solid to gas ratio refers to the pounds of carbide per cubic foot of air (STP). The pressures shown are the pressures at the regulator, corresponding to regulator 28 in Fig. 1. The Fig. 9 tests were made using twenty feet of /2 feed line. The Fig. 10 tests were made using twenty feet of a feed line. The curves of Figs. 9 and 10 are merely illustrative and will vary with the particular set-up such as different length hoses and other obvious factors.

The preferred pressure differential between the pressure in the hopper and the pressure in the inductor is less than 30 pounds per square inch when feeding calcium carbide. The calcium carbide passes a twenty mesh (Tyler) screen and preferably about two-thirds is retained on a 100 mesh screen. The inlet pressure is preferably about 10 p. s. i. g. or above.

With reference to both embodiments, it is to be noted that an appreciable annular space exists about the shields 52 and 92 and that the substantially unrestricted or unobstructed (non-pressure-reducing) inductors 47 and 83 picked up powder from a vertically extending inlet having an effective cross-sectional area appreciably less than that of the respective inductors. Smooth and uniform feeding without slugging or breathing are provided by both embodiments. Both inductors 47 and 83 constitute a form of tube-like, horizontal, unobstructed members. It can also be emphasized, as a notable feature, that both embodiments move powder upwardly through a passage that is in opposition to gravity to be picked up by gas stream moving horizontally. It is also to be noted that by increasing the pressure on the powder and decreasing the pressure in the inductor increased feed rates are accomplished and that the basic requirement for powder pick-up is that the hopper pressure exceeds the pressure in the inductor.

It is to be noted that the instant invention is especially suitable for conveying particles which pass a 20 mesh screen and preferably at least a large part passes a mesh (Tyler) screen.

Although two embodiments of the invention have been shown and described herein in connection with the dispensing of finely-divided materials, it will be understood that there may be various changes and modifications of particular forms shown without departure from the spirit of the invention as defined by the following claims.

We claim:

1. A pneumatic powder feeder for entraining powdered material at variable predetermined feed rates in a flowing gas stream, comprised of a gas-tight hopper having an opening in the bottom thereof, an inductor assembly having an opening at the top thereof attached to the bottom of said hopper and arranged to receive powder from said hopper through said opening in the bottom of the hopper by the action of gravity, said inductor assembly including a small chamber for receiving powder and a tube passing horizontally and completely through said chamber at a location spaced from the bottom of said chamber, said tube having means including a vertical flow path which provide fluid communication between the interior of said tube and said chamber, a pressure-regulated gas supply line connected to said hopper by a first conduit and connected to said tube by a second conduit, said second conduit having an adjustable pressure reducing device therein whereby the pressure in said hopper can be made greater than the pressure in said tube.

2. The powder feeder according to claim 1 and further including the feature that said means including a vertical flow path for providing fluid communication comprises an opening in the bottom of said tube and a short downwardly depending hollow member attached to said tube around said opening.

3. The powder feeder according to claim 1 and further including the feature that said means including a vertical flow path for providing fluid communication includes a fixedly restricted passage therein.

4. A pneumatic powder feeder comprised of .a gas-tight hopper having an opening in the bottom thereof, an inductor assembly having an opening at the top thereof attached to the bottom of said hopper and arranged to receive powder from said hopper through said opening in the bottom of the hopper by the action of gravity, said inductor assembly including .a small cylindrical chamber and a horizontally extending conduit passing through said chamber at a location spaced from the bottom of said chamber, said conduit having a substantially uniform cross-sectional area, said conduit having means including a vertical flow path which provide fluid communication between the interior of said conduit and said chamber, said means including an outlet passage having an effective cross sectional area which is appreciably smaller than said horizontal conduit, a gas supply line connected to said hopper by a first pipe and connected to said tube by a second pipe, said second pipe having a pressure reducing device therein whereby the pressure in said hopper can be made greater than the pressure in said conduit.

5. The powder feeder according to claim 4 and further including the features that said means includes a downwardly depending tube-like structure attached to said conduit and further that an appreciable annular space is formed by the spacing between said structure .and the wall of said chamber.

6. A pneumatic powder feeder comprised of a gas-tight hopper having an opening in the bottom thereof, an inductor assembly having an opening at the top thereof attached to the bottom of said hopper and having means for admitting powder from said hopper into said assembly, said inductor assembly being removably attached to said hopper adjacent said opening so that powder can move into said assembly through said means, said assembly including a cylindrical body part having a tube-like structure extending horizontally across said body part, said structure having a substantially uniform cross-sectional area, said tube-like structure having an opening in the bottom thereof and a pipe-like hollow member depending therefrom so as to form an open passage to said opening, a removable cap closing ofi the bottom of said cylindrical body part, and a pressure-regulated gas supply line connected to said hopper by a first conduit and connected to said tube by a second conduit, said second conduit having an adjustable pressure reducing device therein whereby the pressure in said tube may be varied but is less than the pressure in the hopper.

7. The powder feeder according to claim 6 and further including the feature that said means for admitting powder includes an anti-bridging device extending up into said hopper.

8. Apparatus for entraining powdered material at variable predetermined feed rates in a flowing gas stream comprising a gas-tight powder hopper having an opening and closure therefor, a powder inductor'assembly connected to the bottom of said hopper and constructed and arranged to receive powder from said hopper and to entrain the powder in a gas stream, gas supply means including a first conduit connected to said hopper for admitting a pressure-regulated gas into said hopper and further including a second conduit connected to said powder inductor assembly, said second conduit having a throttle valve therein, said throttle valve having indicator means for indicating different settings of said throttle valve, said gas supply means having a connection conduit adapted to be connected to a source of pressurized gas, and said gas supply means also having a shut-oif valve and then a valved vent adapted to vent to atmosphere downstream of said connection and upstream from said throttle valve whereby the output of said inductor can be stopped downstream from said inductor, said shut-01f valve can be closed and said valve vent opened with the result that the hopper can be easily opened and recharged without adjusting said throttle valve.

References Cited in the file of this patent UNITED STATES PATENTS Roseng-arten July 4, 1905 

